Numerical and experimental investigation of flat-clinch joint strength

The striving for energy savings by lightweight construction requires the combination of different materials with advantageous properties. For joining sheet metal components, clinching offers a good alternative to thermal joining processes. In contrast to thermal joining processes, the microstructure in the joining zone remains largely unaffected. Conventional clinch joints, however, have a protrusion on the underside of the joint, which restricts their use in functional and visible surfaces. Flat-clinching minimizes this disadvantage by using a flat anvil instead of a die. Due to the flatness on the underside, it can be used in visible and functional surfaces. This paper deals with the increase of joint strength by using an auxiliary joining element (AJE) in the second forming stage. To achieve optimum improvement in the joint strength of an aluminum Al99.5 H14 sheet metal joint and to save costs, the AJE was varied numerically in terms of volume, material and basic shape. The geometric parameters (e.g., interlocking f and neck thickness tn) do not allow direct derivation of the joint strength. For this reason, the 2D clinch model was extended for the first time to include 3D load models (cross tension, shear tension). To validate the numerical results, optimized flat-clinch joints with AJE and the associated load tests were implemented experimentally. The numerical models were used to improve the process development.

Effects of Different Types of Interlayers on the Interfacial Reaction Mechanism at the Cu Side of Al/Cu Lap Joints Obtained by Laser Welding/Brazing

The influence of tin foil and Ni coatings on microstructures, mechanical properties, and the interfacial reaction mechanism was investigated during laser welding/brazing of Al/Cu lap joints. In the presence of a Zn-based filler, tin foil as well as Ni coating strengthened the Al/Cu joints. The tin foil only slightly influenced the joint strength. It considerably improved the spreading/wetting ability of the weld filler; however, it weakened the bonding between the seam and the Al base metal. The Ni coating considerably strengthened the Al/Cu lap joints; the highest tensile strength was 171 MPa, which was higher by 15.5% than that of a joint without any interlayer. Microstructure analysis revealed that composite layers of Ni3Zn14–(τ2 Zn–Ni–Al ternary phase)–(α-Zn solid solution)–Al3Ni formed at the fusion zone (FZ)/Cu interface. Based on the inferences about the microstructures at the interfaces, thermodynamic results were calculated to analyze the interfacial reaction mechanism. The diffusion of Cu was limited by the Ni coating and the mutual attraction between the Al and Ni atoms. The microstructure comprised Zn, Ni, and Al, and they replaced the brittle Cu–Zn intermetallic compounds, successfully strengthening the bonding of the FZ/Cu interface.

A study on the effect of process parameters on the joint strength and leak tightness in electromagnetically assisted adhesive Cu-SS tube-to-tube joining through statistical analysis

This work studies an improved hybrid joining technique combining electromagnetic forming and adhesive joining to create a leak-tight Cu-SS tube-to-tube joint named as electromagnetically assisted adhesive joining (EAAJ). An experimental investigation is performed considering three discharge energy (3.9 kJ, 4.4 kJ and 5.0 kJ), four adhesive application lengths (20 mm, 15 mm, 10 mm and 5 mm), three adhesives (Loctite 638, Loctite 567, and Loctite SI 596) and four curing times (24 hours, 48 hours, 96 hours and 120 hours) as process parameters. The mechanical properties of the joints are investigated using testing techniques like pull-out, compression, and micro-hardness tests. An increase in joint strength is observed with the decrease in adhesive application length and increase in curing time. Maximum joint strength, 90% of the base copper tube strength, is obtained in the case of Loctite 638, with 5 mm of adhesive application length, 5.0 kJ of discharge energy and 96 hours of curing time. Furthermore, a three-way analysis (3-way ANOVA) of variance technique is implemented to calculate the contribution of the three factors (discharge energy, adhesive application length, type of adhesives) on the joint strength. A cohesive and adhesive failure mode combination leading to sliding failure mode is observed as a joint failure mechanism during pull-out and compression testing. A leak testing setup has been developed to investigate the joint’s leak tightness by an air pressure decay test. An increment in leak tightness by 1000 times is observed in 638 EAAJ samples compared to samples joined without adhesives. A 3-way ANOVA analysis is also performed to calculate the contribution of different factors on leak tightness of the joint. Micro-hardness is observed to be increased near the joint interface compared to the base metal. Deformation analysis has highlighted the impact of field shaper slit causing a non-uniformity in radial deformation in the circumferential direction and leading to non-uniform circumferential accumulation of adhesive.